Propylene resin composition

ABSTRACT

A propylene resin composition is constructed so as to contain (A) a propylene-α-olefin random copolymer with the content of a propylene unit of 99.1 to 99.9% by weight, and (B) a propylene-α-olefin random copolymer with the content of a propylene unit of 70 to 90% by weight, in the specified proportion, and to have the specified loss tangent (tan δ) and storage elastic modulus (E′), in the temperature dependence of dynamic viscoelasticity. Thereby, the propylene resin composition is provided, suitable as a raw material for shaped article having a well-balanced combination of transparency, stress-whitening resistance; impact resistance at low temperatures, and further heat resistance.

TECHNICAL FIELD

This invention relates to propylene resin compositions, and moreparticularly to propylene resin compositions having a well-balancedcombination of transparency, stress-whitening resistance and impactresistance at low temperatures, and further having good heat resistance.

BACKGROUND ART

Polypropylene resins have been used in a wide variety of fields, becauseor their relatively low cost and excellent thermal and mechanicalcharacteristics. In general, however, propylene homopolymers have highstiffness, but poor impact resistance, especially at low temperatures.To improve the impact resistance at low temperatures of propylenehomopolymers, a propylene block copolymer composition comprising apropylene homopolymer component as initially produced and anethylene-propylene random copolymer component as subsequently producedhas been extensively employed in various industrial fields includingautomobiles and household appliances.

These conventional propylene block copolymer compositions are excellentin impact resistance, but inferior in transparency as compared withhomopolymers, and have large whitening when subjected to impact. As amethod to improve the disadvantage of whitening when subjected to impactin the propylene block copolymer composition, there have been proposed amethod of increasing the ethylene content in the copolymer and a methodof adding polyethylene to the propylene block copolymer composition.Both methods are excellent in improving impact resistance, but have aproblem, i.e, they reduce the transparency of the product.

JP-A-5-331327 discloses a polymer composition comprising a propyleneblock copolymer composition with a specified ratio of the intrinsicviscosity of a propylene homopolymer component to that of an ethylenepropylene random copolymer component. JP-A-6-145268 discloses a polymercomposition with a specified intrinsic viscosity of a propylenehomopolymer component, a specified ratio of the intrinsic viscosity of apropylene homopolymer component to that of an ethylene propylenecopolymer component and a specified ethylene content in the ethylenepropylene random copolymer component. JP-A-56-72042 and JP-A-57-63350disclose a polyolefin resin composition wherein an ethylene-propylenecopolymer containing a small amount of ethylene is blended with anotherethylene-propylene copolymer. JP-A-10-87744 discloses a propylene resincomposition wherein a small amount of ethylene is incorporated in apropylene homopolymer component in the ethylene-propylene blockcopolymer.

DISCLOSURE OF THE INVENTION

Shaped articles made from these polymer compositions have been moreimproved than conventional propylene block copolymer compositions inrespect of the stress-whitening resistance and transparency, butadditional improvements have been required.

An object of the invention is to provide a propylene resin compositionhaving a well-balanced combination of transparency, stress-whiteningresistance and impact resistance at low temperatures and further heatresistance characteristics.

As a result of earnest investigations to attain the above-describedobjects, we have found that a propylene resin composition wherein (A) apropylene-α-olefin random copolymer containing a specified amount ofα-olefin unit and (B) a propylene-α-olefin random copolymer having thecontent of α-olefin unit different from the random copolymer (A) arecomposed in a specified composition has a well-balanced combination oftransparency, stress-whitening resistance and impact resistance at lowtemperatures, and further good heat resistance characteristics. Thetemperature dependence of dynamic viscoelasticity of the resincomposition is such that, the loss tangent (tan δ) and the storageelastic modulus (E′) meet certain conditions. The present invention wasthus completed.

Thus the present invention relates to a propylene resin compositioncomprising 80 to 40% by weight, based on the weight of the composition,of (A) a propylene-α-olefin random copolymer with the content of apropylene unit of 99.1 to 99.9% by weight, and 20 to 60% by weight,based on the weight of the composition, of (B) a propylene-α-olefinrandom copolymer with the content of a propylene unit of 70 to 90% byweight, and the temperature dependence of dynamic viscoelasticity of thecomposition is such that the composition shows only one peak of losstangent (tan δ) in the temperature range of −80° C. to 80° C., and thetemperature at which the storage elastic modulus (E′) is 1×10⁸ dyn/cm²or less is not less than 150° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow sheet showing a continuous polymerization apparatusused in the Examples and Comparative Examples. In the reference numbersused in FIG. 1 and 10 refer to a polymerization reactor, 2 and 7 referto a hydrogen piping, 3 and 6 refer to a raw material mixing gas piping,4 and 8 refer to an unreacted gas piping, 5 and 9 refer to a polymerremoval piping, and 11 refers to an active inhibitor addition piping.

FIG. 2 is a chart of storage elastic modulus (E′) and loss tangent (tanδ) measured, relating to Example 1.

FIG. 3 is a determined chart of storage elastic modulus (E′) and losstangent (tan δ) relating to Comparative Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

In the propylene resin composition, the propylene-α-olefin randomcopolymer (A) contains 99.1-99.9% by weight of a propylene unit and0.9-0.1% by weight of an α-olefin unit other than propylene.

If the content of a propylene unit in the copolymer (A) is too low,shaped articles made from such propylene resin composition have lowerheat resistance characteristics. If the content of the propylene unit istoo high, the stress-whitening resistance and transparency of the shapedarticles become insufficient. It is particularly preferred that thepropylene-α-olefin random copolymer (A) constituting the propylene resincomposition of the present invention contains 99.5-99.9% by weight of apropylene unit and 0.5-0.1% by weight of an α-olefin unit other thanpropylene.

α-olefins constituting the α-olefin unit contained in thepropylene-α-olefin random copolymer (A) can include ethylene, 1-butene,1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-penteneand 3-methyl-1-pentene. One or more olefins may be used. Ethylene and1-butene are preferable from a viewpoint of manufacturing cost.

In the propylene resin composition of the present invention, thepropylene-α-olefin random copolymer (B) contains 70-90% by weight of apropylene unit and 30-10% by weight of an α-olefin unit other thanpropylene. If the content of propylene unit in the copolymer (B) is toohigh, shaped articles made from such composition become insufficient inimpact resistance at low temperatures. If the propylene unit content istoo low, shaped articles have a lower transparency. Thepropylene-α-olefin random copolymer (B) constituting the propylene resincomposition of the present invention contains preferably 70-85% byweight of a propylene unit and 30-15% by weight of an α-olefin unitother than propylene, most preferably 75-85% by weight of a propyleneunit and 25-15% by weight of an α-olefin unit other than propylene.

α-Olefins constituting the α-olefin unit contained in thepropylene-α-olefin random copolymer (B) can include the same compoundsas α-olefins contained in the copolymer (A). Ethylene and 1-butene arepreferable.

The propylene resin composition of the present invention comprises 80 to40% by weight, based on the weight of the composition, of (A) apropylene-α-olefin random copolymer and 20 to 60% by weight, based onthe weight of the composition, of (B) a propylene-α-olefin randomcopolymer. If the content of the copolymer (A) is too high, the impactresistance at low temperatures becomes insufficient. If the content ofthe copolymer (A) is too low, the stiffness lowers remarkably.

It is particularly preferred that the propylene resin composition of thepresent invention comprises 80 to 50% by weight of (A) apropylene-α-olefin random copolymer and 20 to 50% by weight of (B) apropylene-α-olefin random copolymer.

The propylene resin composition of the present invention has atemperature dependence of dynamic viscoelasticity such that it showsonly one peak of loss tangent (tan δ) in the temperature range of −80°C. to 80° C. When the propylene resin composition has two or more peaksof loss tangent in such temperature range, it shows that thecompatibility of each component constituting such composition is notsufficient. Shaped articles produced using this component do not exhibitsuch transparency and stress-whitening resistance as desired in thepresent invention.

When two different components exist together, plural peaks of losstangent will appear. As the compatibility of each component increases,the plural peaks will converge gradually into a single peak. However, itis considered that the composition of the present invention comprising(A) a propylene-α-olefin copolymer and (B) a propylene-α-olefincopolymer with different contents of propylene unit from each other canachieve the effect desired in the present invention by constituting thepeak of loss tangent so as to have only one peak in the abovetemperature range. The advantage of the invention is such that much ofthe characteristics which each component brings individually aremaintained while a strong characteristic (loss tangent) is united into asingle peak.

In addition, the propylene resin composition of the present inventionhas a temperature dependence of dynamic viscoelasticity such that thetemperature at which the storage elastic modulus (E′) lowers to 1×10⁸dyn/cm² or less is 150° C. or more, although the storage elasticmodulus, which is an index of dynamic viscoelasticity, lowers with thetemperature rise.

When the temperature is less than 150° C., shaped articles made fromsuch composition does not exhibit desired heat resistancecharacteristics. When the temperature is 155° C. or more, shapedarticles made from such propylene resin composition have more preferableheat resistance characteristics.

The storage elastic modulus of the propylene resin composition lowersrapidly, when the temperature of the composition rises up mere thanabove a certain temperature. On the other hand, lowering of storageelastic modulus of the composition, i.e., change of dynamic viscoelasticperformance, is gentle in the temperature range where the storageelastic modulus exceeds 1×10⁸ dyn/cm². Lowering of storage elasticmodulus (E′) to 1×10⁸ dyn/cm² or less signifies a fatal loss in thedynamic viscoelastic performance. The significant aspect of theinvention that the temperature at which the storage elastic modulus (E′)lowers to 1×10⁸ dyn/cm² or less is not less than 150° C. signifies thatlowering in the performance of dynamic viscoelasticity with thetemperature rise can be maintained as a gentle lowering. That is, itshows a heat resistant performance in the dynamic viscoelasticity.

The propylene resin composition of the present invention can be producedsuitably, when the intrinsic viscosity (hereafter referred to as[η]_(B)) as determined in tetralin at 135° C. for the propylene-α-olefinrandom copolymer (B) constituting the composition is in the range of 0.5to 2.0 dl/g, particularly 1.0 to 2.0 dl/g, more preferably 1.3 to 2.0dl/g.

Since the intrinsic viscosity [η]_(B) of the propylene-α-olefin randomcopolymer (B) cannot be directly measured, it is calculated from theintrinsic viscosity (hereafter referred to as [η]_(A)) of thepropylene-α-olefin random copolymer (A) and the intrinsic viscosity(hereafter referred to as [η]_(WHOLE)) of the propylene resincomposition as a final product which can be directly measured, and theweight % (hereafter referred to as W_(B)) of the propylene-α-olefinrandom copolymer (B), in accordance with the following equation.

[η]_(B)={[η]_(WHOLE)−(1−W _(B)/100) [η]_(A)}/(W _(B)/100)

The propylene resin composition of the present invention can be usedsuitably as a raw material for the production of shaped articles whichare excellent in transparency, stress-whitening resistance, impactresistance at low temperatures and have further heat resistancecharacteristics.

The propylene resin composition of the present invention may be producedby any suitable method, but it can be suitably produced by a two-stagecontinuous polymerization process in a vapor phase.

The two-stage continuous polymerization process comprises continuouslyconducting the first polymerization step wherein propylene and otherα-olefins than propylene are copolymerized preferably in a vapor phasein the presence of a catalyst containing a catalyst component forpolyolefin manufacture to produce a prescribed amount of thepropylene-α-olefin random copolymer (A) having the specified compositionratio, and successively conducting the second polymerization stepwherein propylene and other α-olefins than propylene are copolymerizedby varying the composition ratio to produce a prescribed amount of theremaining propylene-α-olefin random copolymer (B).

The catalyst used in the above-mentioned process is not limited to aparticular catalyst. A variety of catalyst components such as titaniumand metallocene type catalyst components can be used to produce thecomposition.

As the catalyst components for polyolefin manufacture, those with anaverage particle size of 30-300 μm, preferably 30-150 μm are used. Ifthe average particle size of the catalyst component for polyolefinmanufacture is too small, the powder flowability of the resultantpropylene resin powder composition is impaired remarkably; this tends tocontaminate the polymerization system by adhesion of the powder to thepolymerization reactor wall and the agitator blade, and also creates adifficulty in conveying the powder discharged from the polymerizationreactor. This leads to a hindrance to stable production.

Preferably, the catalyst component for polyolefin manufacture has aparticle size distribution with not more than 3.0 of the degree ofuniformity. If the degree of uniformity is larger, the flowability ofthe propylene resin powder composition will worsen, with the difficultyin continuously stable production.

A stereoregular catalyst comprising the above-described catalystcomponent for polyolefin manufacture, an organoaluminum compound,optionally in combination with an organosilicon compound is used in thecopolymerization of propylene and other α-olefins than propylene in thefirst polymerization step. Preferably, the catalyst is used afterpreactivation by reacting the catalyst component for polyolefinmanufacture with small amounts of α-olefins.

Preactivation of the catalyst component for polyolefin manufacture canbe performed in the presence or absence of similar organoaluminumcompound to that used in the polymerization. In case where thetransition metal in the catalyst component for polyolefin manufacture istitanium, the organoaluminum compound used in the preactivation is usedusually in the range of 0.1-40 mols, preferably 0.3-20 mols per mol oftitanium atom, depending on the type of the catalyst component used forpolyolefin manufacture. 0.1-100 grams, preferably 0.5-50 grams ofα-olefins per gram of the catalyst component for polyolefin manufactureis reacted in an inert solvent using such catalyst at 10-80° C. over aperiod of 10 minutes to 48 hours.

In the preactivation, an organosilicon compound similar to that used inthe polymerization may be used if necessary, in the range of 0.01-10moles per mol of the organoaluminum compound.

α-Olefins used in the preactivation of the catalyst component forpolyolefin manufacture include ethylene, propylene, 1-butene, 1-pentene,1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene,1-octadecene, 1-eicosene, 4-methyl-1-pentene, 3-methyl-1-pentene and thelike. These may be alone or a mixture of two or more compounds.

To control the molecular weight of the polymer produced during thepolymerization, a molecular weight modifier such as hydrogen can be usedtogether.

Inert solvents used in the preactivation of the catalyst component forpolyolefin manufacture are those not affecting the polymerizationreaction remarkably, which include liquid saturated hydrocarbons such ashexane, heptane, octane, decane, dodecane and liquid paraffin, andsilicon oils having dimethylpolysiloxane structure. These inert solventsmay be either a single solvent of one solvent or a mixed solvent of twoor more solvents.

The inert solvents are preferably used after removal of impurities suchas moisture and sulfur compound, which have a bad influence on thepolymerization.

The propylene resin composition of the present invention is producedsuitably by continuously conducting the first polymerization stepwherein propylene and other α-olefins than propylene are copolymerizedin a vapor phase in the presence of a catalyst containing a catalystcomponent for polyolefin manufacture which has been preactivated in theabove process, and successively conducting the second polymerizationstep wherein propylene and α-olefins are copolymerized by varying theratio of propylene used in the first polymerization step.

The first polymerization step, without limitation to a vapor phasepolymerization, can employ a slurry polymerization and a bulkpolymerization. The successive second polymerization step is preferablya vapor phase polymerization, and so preferably the first polymerizationstep may also employ a vapor phase polymerization. In case where slurryand bulk polymerizations are employed as the second polymerization step,the copolymer needs to be dissolved out in a solvent, which tends tomake continuation of stable operation difficult.

For the polymerization conditions of the propylene-α-olefin randomcopolymer (A), propylene and other α-olefins than propylene are suppliedunder the conditions including a polymerization temperature of 20-120°C., preferably 40-100° C., a polymerization pressure of ambient pressureto 9.9 MPa, preferably 0.59-5.0 MPa, in the presence of a stereoregularcatalyst comprising the catalyst component for polyolefin manufacture,an organoaluminum component and optionally an organosilicon compound,while mixing and stirring prescribed amount of powders, thereby carryingout the polymerization of the propylene-α-olefin random copolymer (A).The use ratio (molar ratio) of the organoaluminum compound to thecatalyst component for polyolefin manufacture is Al/Ti=1-500, preferably10-300 for the titanium catalyst component used, depending on the typeof catalyst component used for polyolefin manufacture. In this case, amol number of the titanium catalyst component refers to a gram atom ofsubstantial Ti present in the titanium catalyst component. The use ratio(molar ratio) of the organosilicon compound optionally used to theorganoaluminum compound is Al/Si=1-20 for the titanium catalystcomponent used, depending on the type of catalyst component used forpolyolefin manufacture.

The propylene-α-olefin random copolymer (A) is produced so that thecontent of a propylene unit is 99.1 to 99.9% by weight and 80-40% byweight of the propylene-α-olefin random copolymer (A) is contained inthe composition.

The composition of the present invention is suitably obtained when theintrinsic viscosity [η]_(B) of the propylene-α-olefin random copolymer(B) is 0.5 to 2.0 dl/g. Preferably, the present composition is furthercharacterized in that the intrinsic viscosity of the propylene-α-olefinrandom copolymer (A) is in the range of 0.5 to 4.0 dl/g and theresultant composition meets the requirements for “storage elasticmodulus” and “loss tangent” in the present invention.

The intrinsic viscosity can be controlled by using a molecular weightmodifier such as hydrogen at the time of polymerization. After thepolymerization of the propylene-α-olefin random copolymer (A), part ofthe produced powder is taken out and the intrinsic viscosity [η]_(A) ismeasured.

Subsequent to the polymerization of the propylene-α-olefin randomcopolymer (A), the second polymerization step can be conducted whereinpropylene and other α-olefins than propylene are copolymerized byvarying the composition ratio of the mixed monomer in the firstpolymerization step, under the conditions including a polymerizationtemperature of 20-120° C., preferably 40-100° C., a polymerizationpressure of ambient pressure to 9.9 MPa, preferably 0.59-5.0 MPa, toproduce the propylene-α-olefin random copolymer (B). Thepropylene-α-olefin random copolymer (B) is adjusted so that the contentof α-olefin unit in the copolymer is from 30 to 10% by weight, bycontrolling a gas molar ratio of α-olefin nonomer and propylene monomerin the comonomer gas used.

The weight of the propylene-α-olefin random copolymer (B) is adjusted sothat it is 20 to 60% by weight based on the weight of the composition,by controlling the polymerization time and using a polymerizationactivity modifier such as carbon monoxide, hydrogen sulfide or the like.The molecular weight of the propylene-α-olefin random copolymer (B) isadjusted so that the intrinsic viscosity [η]_(B) of thepropylene-α-olefin random copolymer (B) is preferably 0.5 to 2.0 dl/g,by using a molecular weight modifier such as hydrogen upon thepolymerization of the copolymer (B).

The polymerization process may be any of batch, semi-continuous andcontinuous processes, but a continuous polymerization is industriallypreferable.

After the completion of the second polymerization step, any residualmonomer can be removed from the polymerization system to prepare aparticulate polymer. The resultant polymer is subjected to themeasurement of the intrinsic viscosity ([η]_(WHOLE)) and the content ofα-olefin.

The propylene resin compositions of the present invention can be used asraw materials for shaped articles having various shapes formed by avariety of shaping methods such as injection, extrusion, inflation,calendaring or the like. In molding, the propylene resin composition maybe blended, if necessary, with inorganic fillers such as talc, calciumcarbonate, silica and mica, and organic and inorganic pigments which areused in conventional polyolefins. Further, known additives can be added,if necessary, such as antioxidants, neutralizers, weathering agents,antistatic agents, lubricants, foaming agents, flame retardants andtransparent nucleating agents.

EXAMPLES

The invention is further illustrated by the following examples andcomparative examples, but not limited thereto.

1) Method for the Measurement of Various Physical Properties

The methods for the measurement of physical properties used in theExamples and Comparative Examples are mentioned below.

a) tan δ δ and E′: They were measured at a frequency of 110 Hz and atemperature rise rate of 2° C./min., using an automatic measuring devicefor dynamic viscoelasticity (trade name: REO VIBRON DDV-III-EP,manufactured by ORIENTEC Co. Ltd.). For the measurement, a plate-like27×10×1 mm test piece was used, which was prepared by melt pressing thepropylene resin composition at 200° C.

b) Intrinsic viscosity (dl/g): It was measured in tetralin(tetrahydronaphthalene) solvent, at a temperature of 135° C., using anautomatic viscometer (trade name: AVS2-type, manufactured by MITSUITOATSU, Co., Ltd.).

c) Particle size (μm) and degree of uniformity of catalyst component forpolyolefin manufacture: The average particle size was determined from aparticle size distribution measured using “Master Sizer” (trade name,manufactured by MALVERN Co. Ltd.). The degree of uniformity was obtainedby dividing a particle size equivalent to a screen opening where theintegrated amount of a sample fallen from a screen opening reached 10%of all samples when the screen opening is gradually shifted from a smallscreen opening to a large screen opening, by a particle size equivalentto a screen opening where the above amount reached 60% of all samples.

d) Content of α-Olefin unit (weight %): It was measured by Infraredabsorption spectroscopy.

e) Melting point: It was measured at a temperature rise rate of 20°C./min., using a differential scanning calorimeter (trade name: DSCDupont 1090, manufactured by Du Pont Company).

2) Preparation of Catalyst Component for Polyolefin Manufacture

a) Catalyst Component for Polyolefin Manufacture (A-1)

95.3 g of anhydrous MgCl₂ and 352 ml of dry EtOH were charged in a SUSautoclave purged with nitrogen, and the mixture was heated to 105° C.with stirring; and the mixture was melted. After stirring for one hour,the resulting liquid was fed into a two-way spray nozzle withpressurized nitrogen (1.1 MPa) heated at 105° C. The flow rate ofnitrogen gas was 38 liter/min. Liquid nitrogen was introduced into aspray tower for cooling the tower, i.e, to keep the temperature in thetower at −15° C. 265 g of the product was collected in cooled hexaneintroduced at the bottom of the tower. According to the analysis of theproduct, the composition of this product was found to be MgCl₂▭6EtOHidentical with the starting solution.

This product was sieved to obtain 205 g of a spherical product having aparticle size of 45-212 μm. The resultant spherical product was dried atroom temperature for 181 hrs., using nitrogen at the flow rate of 3liters/min, to prepare a dry product with the composition of MgCl₂▭1.7EtOH. This product was used as a carrier.

In a glass flask purged with nitrogen, 20 g of the dry carrier, 160 mlof titanium tetrachloride and 240 ml of purified 1,2-dichloroethane weremixed and heated to 100° C. with stirring, 6.8 ml of diisobutylphthalate were added, and the mixture was further heated at 100° C._for2 hrs. A liquid phase part was removed by decantation, washed withpurified hexane and then dried to prepare a catalyst component forpolyolefin manufacture (A-1). The resultant catalyst component forpolyolefin manufacture (A-1) had the average particle size of 115 μm andthe degree of uniformity of 1.80, with the analysis of the followingcomposition: Mg: 19.5% by weight, Ti: 1.6% by weight, Cl: 59.0% byweight.

b) Catalyst Component for Polyolefin Manufacture (A-2)

60 ml of titanium tetrachloride and 40 ml of toluene were charged in aglass flask purged with nitrogen to prepare a mixed solution. Asuspension prepared from 20 g of magnesium diethoxide having an averageparticle size of 42 μm, 100 ml of toluene and 7.2 ml of di-n-butylphthalate was added to the mixed solution kept at 10° C. Subsequently,the temperature of the resulting mixture was elevated from 10° C. to 90°C. over a period of 80 minutes and the mixture was stirred for 2 hrs toallow the reaction to proceed. After completion of the reaction, theresulting solid product was washed four times with 200 ml of toluene at90° C., and 60 ml of additional titanium tetrachloride and 140 ml oftoluene were added. The temperature of the mixture was elevated to 112°C. and the mixture was stirred for another 2 hrs to allow the reactionto proceed. After completion of the reaction, the resultant solidproduct was washed 10 times with 200 ml of n-heptane at 40° C. toprepare a catalyst component for polyolefin manufacture (A-2). Theresultant catalyst component for polyolefin manufacture (A-2) had theaverage particle size of 42 μm and the degree of uniformity of 2.00,with the analysis of the following composition: Mg: 18.9% by weight, Ti:2.2% by weight, Cl: 61.6% by weight.

c) Catalyst Component for Polyolefin Manufacture (A-3)

A mixture of 300 g of magnesium ethoxide, 550 ml of 2-ethylhexyl alcoholand 600 ml of toluene was stirred at 93° C. for 3 hrs under a carbondioxide atmosphere of 0.20 MPa, and further 800 ml of toluene and 800 mlof n-decane were added to prepare a magnesium carbonate solution.

100 ml of the magnesium carbonate solution as prepared above were addedto a mixed solution stirred at 30° C. for 5 minutes, comprising 800 mlof toluene, 60 ml of chlorobenzene, 18 ml of tetraethoxysilane, 17 ml oftitanium tetrachloride and 200 ml of “Isopar G” (trade name,manufactured by EXXSON Co. Ltd.) (isoparaffin hydrocarbon with 10average carbon numbers, b.p. 56-176° C.).

After stirring for additional 5 minutes, 44 ml of tetrahydrofuran wereadded, and the mixture was stirred at 66° C. for one hour. After thestirring was ceased and the supernatant solution was removed, theresulting solid was washed with 100 ml of toluene, 200 ml ofchlorobenzene and 200 ml of titanium tetrachloride were added to theresultant solid, and a mixture was stirred at 135° C. for one hour.After stirring was ceased and the supernatant solution was removed, 500ml of chlorobenzene, 200 ml of titanium tetrachloride and 4.2 ml ofdi-n-butyl phthalate were added, and the mixture was mixed at 135° C.for 1.5 hrs. After the supernatant solution was removed, the solid waswashed with successive, 1200 ml of toluene, 1600 ml of “Isopar G” and800 ml of hexane to prepare a catalyst component (A-3) for polyolefinmanufacture in Comparative Example. The resultant catalyst component forpolyolefin manufacture (A-3) had the average particle size of 24 μm andthe degree of uniformity of 1.64, with the analysis of the followingcomposition: Mg: 17.0% by weight, Ti: 2.3% by weight, Cl: 55.0% byweight.

Example 1 3) Pre-activation of Catalyst Component for PolyolefinManufacture

A stainless steel reaction vessel having an internal volume of 20 litersequipped with slant vanes was purged with nitrogen gas and then chargedat room temperature with 18 liter of a saturated hydrocarbon solventhaving a dynamic viscosity of 70 centistokes at 40° C. (trade name:CRYSTOL-352, manufactured by ESSO Petroleum Co. Ltd.), 1.8 liter ofhexane, 100.6 mmol of triethyl aluminum, 15.1 mmol ofdi-isopropyl-di-methoxysilane and 120.4 g of the catalyst component(A-1) for polyolefin manufacture as prepared above, and the mixture waswarmed to 30° C. Subsequently, the catalyst was pre-activated by feeding240.8 g of propylene while stirring over a period of 3 hrs. The resultof the analysis indicated that 1.9 g of propylene was reacted per 1 g ofthe catalyst component for polyolefin manufacture.

4) First Polymerization Step

In the flow sheet shown in FIG. 1, 0.4 g/hr of the pre-activatedcatalyst, triethyl aluminum as an organoaluminum compound anddi-isopropyl-di-methoxysilane as an organosilicon compound werecontinuously fed to a horizontal type polymerization reactor equippedwith stirring vanes (L/D=6, internal volume 100 lit.), under such acondition that an Al/Si molar ratio was 6. A mixed gas of propylene andethylene in the indicated molar ratio as shown in Table 1 wascontinuously fed, while maintaining the conditions including thereaction temperature of 60° C., the reaction pressure of 2.1 MPa and thestirring speed of 35 rpm. Further, hydrogen gas was continuously fedthrough piping 2 so that the hydrogen concentration in the vapor phasewithin the polymerization reactor was kept at the hydrogen/propylenemolar ratio shown in Table 1, to produce the propylene-α-olefincopolymer (A).

The reaction heat was removed as heat of vaporization of a raw material,propylene fed through piping 3. Unreacted gas discharged from thepolymerization reactor was cooled and condensed outside the reactionsystem via piping 4 and returned to polymerization reactor 1.

The resultant propylene-α-olefin random copolymer (A) was continuouslytaken out from the polymerization reactor 1 via piping 5 so that thepolymer occupied 50% by volume of the reactor, and then it was fed to apolymerization reactor 10 in the second polymerization step. At thistime, a part of the propylene-α-olefin random copolymer (A) wasintermittently taken out from piping 5 and it was used as a sample formeasuring the ethylene content and intrinsic viscosity.

5) Second Polymerization Step

The propylene-α-olefin random copolymer (A) from the firstpolymerization step and a mixed gas of ethylene and propylene werecontinuously fed to a horizontal type polymerization reactor 10 equippedwith stirring vanes (L/D=6, internal volume 100 lit.) to carry out acopolymerization of ethylene and propylene. The reaction conditionsinclude the stirring speed of 25 rpm, the temperature of 55° C. and thepressure of 1.9 MPa. The gas composition in the vapor phase wascontrolled to give the ethylene/propylene molar ratio and thehydrogen/ethylene molar ratio shown in Table 1. Through piping 11,carbon monoxide was supplied as a polymerization inhibitor to controlthe amount of the propylene-α-olefin random copolymer (B) polymerized,and through piping 7 hydrogen gas was supplied to control the molecularweight of the propylene-α-olefin random copolymer (B).

The reaction heat was removed by heat of vaporization of a raw material,liquid propylene supplied from piping 6. Unreacted gas discharged fromthe polymerization reactor was transferred to the outside of thereaction system via piping 8, cooled, condensed and then returned to thesecond polymerization step. The propylene resin composition produced inthe second polymerization step was continuously taken out frompolymerization reactor 10 via piping 9 so that the level of the polymerretained is 50% by volume of the reaction volume. The production rate ofthe propylene resin composition was 8 to 15 kg/hr.

For the propylene-α-olefin random copolymer (A) produced in the firststep and the polypropylene composition produced in the second step,various physical properties were measured. The intrinsic viscosity[η]_(B) of the propylene-α-olefin random copolymer (B) was calculated onthe basis of the above-mentioned equation, using the intrinsic viscosity[η]_(A) of the propylene-α-olefin random copolymer (A) and the intrinsicviscosity [η]_(WHOLE) of the propylene resin composition. The result ofvarious physical properties measured is shown in Table 1. The chart ofstorage elastic modulus (E′) and loss tangent (tan δ) measured is shownin FIG. 2.

Examples 2-5, Comparative Examples 1-4

The above-mentioned catalyst component for polyolefin manufacture (A-2)was used as a catalyst component. The compositions of Examples 2-5 andComparative Examples 1-4 were produced by varying the ethylene/propylenemolar ratio and the hydrogen/propylene molar ratio in the firstpolymerization step as well as the ethylene/propylene molar ratio andthe hydrogen/ethylene molar ratio in the second polymerization step asshown in Tables 1 and 2.

The results of various physical properties measured for the resultantcompositions are shown in Tables 1 and 2. For Comparative Example 2, thechart of storage elastic modulus (E′) and loss tangent (tan δ) measuredis shown in FIG. 3.

Comparative Example 5

The above-mentioned catalyst component for polyolefin manufacture (A-3)was used as a catalyst component. The composition of Comparative Example5 was produced by varying the ethylene/propylene molar ratio and thehydrogen/propylene molar ratio in the first polymerization step as wellas the ethylene/propylene molar ratio and the hydrogen/ethylene molarratio in the second polymerization step as shown in Table 2.

The result of various physical properties measured for the resultantcomposition is shown in Table 2.

6) Production of Injection Molded Articles

0.004 kg of a phenol type heat stabilizer and 0.004 kg of calciumstearate were added to 4 kg of each composition produced in each Exampleand Comparative Example, and they were mixed at room temperature for 2minutes using a high speed stirring mixer (trade name: Henschel mixer).The mixture was granulated into pellets in an extruding granulator witha screw diameter of 40 mm. Then, a JIS type test piece was prepared fromthe pellets using an injection molding machine at the molten resintemperature of 250° C. and the mold temperature of 50° C. The resultingtest piece was conditioned in a chamber kept at 50% humidity and at atemperature of 23° C. for 72 hours, and various physical propertiesthereof were measured according to the following methods. The resultswere shown in Tables 1 and 2.

a) Flexural modulus (MPa): It was measured in accordance with JIS K7203.

b) Haze: It was measured in accordance with ASTM D 1003 using aplate-like 25×50×1 mm test piece conditioned under the above condition.

c) Izod impact value: It was measured in accordance with JIS K 6758 ateach temperature of 0° C. and −20° C.

d) Whitening by impact: A load was fallen, under the followingconditions, on a plate-like 50×50×2 mm test piece conditioned under theabove conditions, using a du Pont impact machine (manufactured by ToyoSeiki Co., Ltd.), and a diameter of whitening area generated on the testpiece by impact was measured.

Tip radius in impact core 0.635 cm Inner diameter of anvil 3.81 cm Load500 g Falling height of load 1 m

TABLE 1 Example 1 2 3 4 5 First polymerization step Polymerization 2 → →→ → pressure MPa Polymerization 60 → → → → temperature ° C. α-Olefincomponent ethylene → → → → Hydrogen/propylene 0.004 0.006 0.005 0.0040.005 (molar ratio) Ethylene/propylene 0.007 0.007 0.006 0.002 0.003(molar ratio) Copolymer (A) Produced amount 67 73 60 56 75 W_(A) wt %Propylene unit content 99.1 99.1 99.2 99.7 99.6 wt % Secondpolymerization step Polymerization 1.9 → → → → pressure MPaPolymerization 55 → → → → temperature ° C. α-Olefin component Ethylene →→ → → Ethylene/propylene 0.14 0.13 0.11 0.11 0.13 (molar ratio)Hydrogen/ethylene 0.52 0.45 0.60 0.62 0.52 (molar ratio) Copolymer (B)Produced amount 33 27 40 44 25 W_(B) wt % Propylene unit 75 77 78 78 77content wt % Intrinsic viscosity [η]_(B) 1.76 1.93 1.66 1.59 1.61Propylene resin composition Number of tan δ peak 1 1 1 1 1 in the rangeof - 80-80° C. Temperature at which 154.6 153.7 154.7 163.5 163.1 E′ is1 × 10⁸ or less ° C. Intrinsic viscosity 1.76 1.93 1.66 1.59 1.61[η]_(WHOLE) Physical properties of shaped article Flexural modulus MPa350 570 450 380 590 Haze % 31 39 32 38 39 Izod impact value NB*¹ 14.1NB*¹ NB*¹ 12.4 (0° C.) kJ/m² (−20° C.) 16 10 18 14 8 Diameter ofwhitening 0 3.2 0 0 3.5 by impact mm Melting point ° C. 156 156 157 161161 *1: Not destructed

TABLE 2 Comparative Example 1 2 3 4 5 First polymerization stepPolymerization 2 → → → → pressure MPa Polymerization 60 → → → →temperature ° C. α-Olefin component — — ethylene → → Hydrogen/propylene0.0035 0.02 0.02 0.006 0.012 (molar ratio) Ethylene/propylene 0 0 0.0020.006 0.029 (molar ratio) Copolymer (A) Produced amount 50 67 67 82 80W_(A) wt % Propylene content 100 100 99.8 99.3 97.0 wt % Secondpolymerization step Polymerization 1.9 → → → → pressure MPaPolymerization 55 → → → → temperature ° C. α-Olefin component Ethylene →→ → → Ethylene/propylene 0.23 0.26 0.26 0.14 0.14 (molar ratio)Hydrogen/ethylene 0.30 0.41 0.40 0.90 0.40 (molar ratio) Copolymer (B)Produced amount 50 33 33 18 20 W_(B) wt % Propylene 66 64 64 75 75content wt % Intrinsic viscosity [η]_(B) 2.59 2.02 2.16 1.54 2.17Propylene resin composition Number of tan δ peak 2 2 2 1 1 in the rangeof - 80-80° C. Temperature at which 164.7 170.7 168.7 154.9 143.7 E′ is1 × 10⁸ or less ° C. Intrinsic viscosity 2.84 2.02 2.08 2.41 2.17[η]_(WHOLE) Physical properties of shaped article Flexural modulus MPa300 570 560 740 510 Haze % 47 53 52 53 45 Izod impact value NB*¹ NB*¹NB*¹ 6.5 10.6 (0° C.) kJ/m² (−20° C.) NB 19 16 3.7 5.4 Diameter ofwhitening 0 14.7 12.7 12.5 12.9 by impact mm Melting point ° C. 165 165162 158 145 *1: Not destructed

INDUSTRIAL UTILIZATION

The shaped articles produced from the propylene resin compositionsatisfying the requirements for physical properties in the presentinvention have excellent transparency, stress-whitening resistance,impact strength at low temperatures, and further heat resistance, andwell-balanced properties thereof. The propylene resin composition of thepresent invention is used suitably in various applications for whichsuch properties are required.

What is claimed is:
 1. A propylene resin composition comprising 80 to40% by weight of (A) a propylene-α-olefin random copolymer with thecontent of a propylene unit of 99.1 to 99.9% by weight, and 20 to 60% byweight of (B) a propylene-α-olefin random copolymer with the content ofa propylene unit of 70 to 90% by weight, wherein the temperaturedependence of dynamic viscoelasticity of the composition is such thatthe composition shows only one peak of loss tangent (tan δ) in thetemperature range of −80° C. to 80° C., and the temperature at whichstorage elastic modulus (E′) is 1×10⁸ dyn/cm² or less is not less than150° C.
 2. The propylene resin composition of claim 1 wherein thetemperature at which E′ is 1×10⁸ dyn/cm² or less is not less than 155°C.
 3. The propylene resin composition of claim 1 wherein the intrinsicviscosity of the propylene-α-olefin random copolymer (B) is in the rangeof 0.5-2.0 dl/g.